I kinda feel like Iceborn should deal magic damage.
Idk, it's always seemed more friendly to magic damage tanks/bruisers than physical, since physicals would usually opt for Triforce instead. Plus, it does feel a little lame that you don't get any damage upgrade with Iceborn anymore, so turning it into magic damage would in a way usually be a mild damage buff without actually changing the scaling.
*edit: and to the people saying things like 'Ez or whoever else would now deal mixed damage': A) Ez already does deal mixed damage to some degree B) It's still a relatively minor amount of damage, something like ~100-120 damage every 2 second. Comparable to Sunfire even if you do manage to proc it immediately as its cd becomes available again. C) Physical champs also wouldn't benefit from their penetration/armor shred with the now-magic damage. D) They also wouldn't be able to leech off of it anymore.